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A227870
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Numbers with equal number of even and odd digits.
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11
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10, 12, 14, 16, 18, 21, 23, 25, 27, 29, 30, 32, 34, 36, 38, 41, 43, 45, 47, 49, 50, 52, 54, 56, 58, 61, 63, 65, 67, 69, 70, 72, 74, 76, 78, 81, 83, 85, 87, 89, 90, 92, 94, 96, 98, 1001, 1003, 1005, 1007, 1009, 1010, 1012, 1014, 1016, 1018, 1021, 1023, 1025
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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Numbers with an odd digit length cannot be in this sequence. - Alonso del Arte, Nov 02 2013
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LINKS
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EXAMPLE
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1009 has 2 even digits (00) and 2 odd digits (19) and so is in the sequence.
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MATHEMATICA
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Select[Range[1025], (d = Differences[Tally[Mod[IntegerDigits[#], 2]]]) != {} && d[[1, 2]] == 0 &] (* Amiram Eldar, Oct 01 2020 *)
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PROG
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(JavaScript)
for (i = 1; i < 5000; i++) {
s = i.toString();
odds = 0; evens = 0;
for (j = 0; j < s.length; j++) if (s.charAt(j)%2 == 0) evens++; else odds++;
if (odds == evens) document.write(i + ", ");
}
(PARI) isok(m) = my(d=digits(m)); #select(x->(x%2), d) == #select(x->!(x%2), d); \\ Michel Marcus, Oct 01 2020
(Python)
def ok(i):
stri = str(i)
se = sum(1 for d in stri if d in "02468")
so = sum(1 for d in stri if d in "13579")
return se == so
def aupto(nn):
alst, an = [None], 0
for n in range(1, nn+1):
while len(alst) < nn+1:
if ok(an): alst.append(an)
an += 1
return alst[1:] # use alst[n] for a(n)
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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